Wire line operations generally relate to the attachment of tubular members to a wellhead through which flexible cables called slick lines and wire lines (electrical conductor cables) and tools connected and/or supported thereby are inserted into the well bore while the well is under pressure.
As those in the art are aware, during operation of an oil or gas well, it often becomes necessary to introduce various tools and instruments into the well bore and operate same within the down hole tubing environment while the well is under pressure. These tools and instruments are ordinarily inserted into the well by using flexible cable or wire lines which may also be insulated electrical conductors that carry electrical power to such down hole instruments and tools. Since very high pressures may exist within the well, the introduction of such tools and instruments is considerably more difficult and there is always the possibility of blowouts or other serious accidents.
In order to conduct the various wire line operations, tools and instruments are introduced into the production string by lowering the tools into the well on flexible cable or wire lines. In the case of electrically operated or actuated tools and instruments, the lowering line or cable often includes electrical conducting wires encased in suitable insulation and armor.
Due to the forces exerted by high well pressures against the tools and cables entering the well, conventional practices use various methods to overcome these forces in order to allow the tools to descend into the well. Such methods generally included adding heavy weights or so-called “sinker bars” having sufficient weight to overcome the opposing pressure forces of the instrument or tool being inserted into the well bore.
A typical wire line setup employs a tubing string or riser attachment adapted for connection to the wellhead above the shut-off valves, the tubing string having size and length to accommodate the tool or instrument length and sufficient sinker bars to overcome the well's pressure. Therefore, in many cases the riser tubing may become quite lengthy. In such cases, the upper end of the riser tubing must be supported by using the derrick elevator cable. A radial housing having a pulley therein is attached to the upper end of the riser, to which is also attached a second vertical tubing string to direct the wire line 180 degrees in a downward direction parallel to the riser tube. The wire line, paid off from a winch spool, is then threaded through the second vertical tubing string, around the radial pulley, out the end of the riser tubing string and connected to the tool or instrument. The instrument or tool is then retracted within the riser via the wire line and the riser assembly is then lifted by the elevator cable attached to the radial pulley housing and attached to the wellhead. In some cases the radial pulley is also electrically or hydraulically powered. In any case, it should be noted that this procedure must be repeated in reverse to retrieve the instrument or tool and must also be repeated with each successive deployment of such tools or instruments. The length and/or size of the riser assembly must be changed to accommodate each new tool or instrument by adding or subtracting riser joints and sinker bars.
Because of the high pressures which may be encountered in the well, instruments and tools and their suspension cable, in accordance with conventional practices, are fed into the well through lubricators, attached to the second vertical riser tubing, which commonly use heavy grease stuffing boxes designed to squeeze tightly about the lowering line or electrical cable in order to prevent escape of the well pressure and to hold the well under control.
These conventional systems have a difficult time in preventing leakage around the conductor cable or wire line. Obviously, the greater the well pressure, the tighter compression around the wire line must be. However, any such additional pressure results in additional friction on the wire line or cable, thus preventing the tool string from freely descending into the well bore. Higher compression applied to the wire line will also often result in serious damage to the slick line or to the wire line electrical conductors. Thus, stuffing box arrangements are actually self-defeating.
Although various apparatus have been disclosed by the prior art in which wellhead attachments are disclosed that teach the use of elongated closed casing or housing structures in which the tool string, including the entire cable or wire line supply, is enclosed in a manner whereby the housing structure is subjected to the well bore pressure, such apparatus have not gained wide spread acceptance in the art due to several disadvantages. The wellhead riser attachment and pressurized wire line spool assemblies only allows the riser assembly to be configured in a single plane and do not provide for offsets and multiple radial bends between the well head and the cable spool assembly.
Further, the prior art pressurized wire line spool assemblies fail to provide a satisfactory method for making a rotary electrical connection between the potentially explosive atmosphere of the wire line spool and the electrical supply leading to the down hole instruments. In addition, no provisions are made in the prior art pressurized wire line spool assemblies for easily adding or changing the wire or cable within a fully enclosed spool without extensive disassembly of the pressurized spool housing.
When it is considered that often tools and instruments must be lowered many thousands of feet into and withdrawn from a well, it will be obvious that the difficulty of running tools rapidly, efficiently, and safely under high pressures will be greatly intensified.
Still further, translating the spool within a pressurized spool housing while rotating the spool under pressure is very difficult in practice, as is maintaining pressure integrity under such high pressures with multiple housing penetrations as required by the prior art.
Accordingly, it is a primary object of the present invention to provide a wire line riser attachment for wellheads by which the various difficulties heretofore encountered in inserting and operating flexible cable-supported tool strings in high pressure wells will be obviated or eliminated.
A further object is to provide a wellhead attachment which includes a pressure-tight housing enclosing a cable-supply reel, cable measuring devices, and tools to be inserted into the well under well pressures, and means for driving the cable-supply reel from the exterior of the housing.
Another object of the invention is to provide a pressure-tight riser assembly having off-set pivotal radial connections for connection between the wellhead and the pressurized cable-supply reel.